1. Field of the Invention
The present invention relates to an electron-emitting device, an electron source using the electron-emitting devices, an image-forming apparatus, such as display devices or the like, constructed using the electron source, and methods for producing them.
2. Related Background Art
The conventionally known electron-emitting devices are roughly classified under two types; thermionic cathodes and cold cathodes. The cold cathodes include field emission type (hereinafter referred to as xe2x80x9cFE typexe2x80x9d) electron-emitting devices, metal/insulator/metal type (hereinafter referred to as xe2x80x9cMIM typexe2x80x9d) electron-emitting devices, surface conduction type electron-emitting devices, and so on.
Examples of the known FE type devices include those disclosed in the following: W. P. Dyke and W. W. Dolan, xe2x80x9cField emission,xe2x80x9d Advance in Electron Physics, 8, 89 (1956); C. A. Spindt, xe2x80x9cPhysical Properties of thin-film field emission cathodes with molybdenum cones,xe2x80x9d J. Appl. Phys., 47, 5248 (1976); M. W. Geis, xe2x80x9cElectron field emission from diamond and other carbon materials after H2, O2, and Cs treatmentxe2x80x9d Appl. Phys. Lett. 67 (9) (1995); W096/35640; Ken Okano, xe2x80x9cLow-threshold cold cathodes made of nitrogen-doped chemical-vapor-deposited diamond,xe2x80x9d Nature, Vol. 381, 1996; A. J. Amaratunga, xe2x80x9cNitrogen containing hydrogenated amorphous carbon for thin-film field emission cathodes,xe2x80x9d Appl. Phys. Lett., 68 (18) (1996); A. Weber, xe2x80x9cCarbon based thin film cathodes for field emission displays,xe2x80x9d J. Vac. Sci. Technol. A16 (3) (1998); Eung Joon Chi, xe2x80x9cEffects of heat treatment on the field emission property of amorphous carbon nitride,xe2x80x9d J. Vac. Sci. Technol. B16 (3) (1998), and so on.
Examples of the known MIM type devices include those disclosed in C. A. Mead, xe2x80x9cOperation of Tunnel-Emission Devices,xe2x80x9d J. Appl. Phys., 32, 646 (1961), and so on.
Examples of the surface conduction electron-emitting devices include those disclosed in M. I. Elinson, Radio Eng. Electron Phys., 10, 1290 (1965), and so on.
The surface conduction electron-emitting devices utilize such a phenomenon that electron emission occurs when electric current is allowed to flow in parallel to the surface in a thin film of a small area formed on a substrate. Examples of the surface conduction electron-emitting devices reported heretofore include those using a thin film of SnO2 by Elinson cited above and others, those using a thin film of Au (G. Ditmmer: xe2x80x9cThin Solid Films,xe2x80x9d 9, 317 (1972)), those using a thin film of In2O3/SnO2 (M. Hartwell and C. G. Fonstad: xe2x80x9cIEEE Trans. ED Conf.,xe2x80x9d 519, (1975)), those using a thin film of carbon (Hisashi Araki et al.: Shinku (Vacuum), Vol. 26, No. 1, p22 (1983)), and so on.
A typical device configuration of these surface conduction electron-emitting devices is the device structure of M. Hartwell cited above, which is shown in FIG. 18. In the same drawing, numeral 1 designates an electrically insulative substrate. Numeral 4 denotes an electrically conductive film, which is, for example, a thin film of a metal oxide formed in an H-shaped pattern and in which an electron-emitting region 5 is formed by an energization operation called xe2x80x9cformingxe2x80x9d described hereinafter. In the drawing the gap Lxe2x80x2 is set to 0.5 to 1 mm and the width Wxe2x80x2 to 0.1 mm.
In these surface conduction electron-emitting devices, it was common practice to preliminarily subject the conductive film 4 to the energization operation called the forming, thereby forming the electron-emitting region 5. Namely, the forming is an operation for applying a dc voltage or a very slowly increasing voltage, for example at the increasing rate of about 1 V/min, to the both ends of the conductive film 4 to locally break, deform, or modify the conductive film, thereby forming the electron-emitting region 5 in an electrically higher resistance state than the resistance in the surroundings. In the electron-emitting region 5 a fissure is created in part of the conductive film 4 and electrons are emitted from near the fissure.
In the surface conduction electron-emitting device after the aforementioned forming operation, electrons are emitted from the above-stated electron-emitting region 5 when the current flows in the device with application of the voltage to the conductive film 4 including the electron-emitting region 5.
On the other hand, for example, as disclosed in Japanese Patent No. 2,836,015, No. 2,903,295, etc., the device after the forming is sometimes subjected to a treatment called an activation operation. The activation operation is a step by which remarkable change appears in the device current If and in the emission current Ie.
The activation step can be performed by repeatedly applying pulse voltage to the device, as in the case of the forming operation, under an ambience containing an organic substance. This operation causes a film mainly containing carbon or a carbon compound to be deposited from the organic substance existing in the ambience onto the electron-emitting region of the device and the vicinity thereof, so as to induce outstanding change in the device current If and in the emission current Ie, thereby achieving better electron emission characteristics.
FIGS. 20A and 20B are schematic diagrams to show the electron-emitting device disclosed in the above publications. In FIGS. 20A and 20B, reference numeral 1 designates an electrically insulating substrate, 2 and 3 electrodes, 4 the aforementioned electrically conductive film, 10 the film mainly containing carbon or the carbon compound, formed by the aforementioned activation operation, and 5 the electron-emitting region.
Since the surface conduction electron-emitting device described above is simple in the structure and easy in the production, it has the advantage of capability of forming an array of many devices across a large area. A variety of applications have been investigated heretofore in order to take advantage of this property. For example, such applications include charged beam sources, display devices, and so on.
An example of the application wherein a lot of surface conduction electron-emitting devices are arrayed is an electron source in which the surface conduction electron-emitting devices are arrayed in parallel and a lot of rows are arranged, each row including the surface conduction electron-emitting devices whose two terminals are connected to respective wires (for example, Japanese Patent Application Laid-Open No. 64-31332, No. 1-283749, and No. 2-257552).
Particularly, in the field of the image-forming apparatus such as the display devices and the like, flat panel display devices using liquid crystals are becoming widespread in recent years, in place of the CRTs, but they are not of a self-emission type. Therefore, they had the problem that a back light or the like was required, for example. Therefore, there were desires for development of the display device of the self-emission type.
When the image-forming apparatus is constructed as a display device in which an electron source comprised of a lot of surface conduction electron-emitting devices is combined with a fluorescent material for emitting visible light with reception of electrons emitted from the electron source, the apparatus, even of the large area, can be produced relatively readily and is the emissive display with excellent quality of display.
An object of the present invention is to provide a configuration of the surface conduction electron-emitting device capable of realizing highly efficient and stable electron emission characteristics, an electron source and an image-forming apparatus using it, and methods for producing them.
The inventors have been conducted intensive and extensive research in order to solve the above object and came to accomplish the present invention, based on such knowledge that the electron emission efficiency of the surface conduction electron-emitting device varied large, depending upon the quality of the carbon-containing film (carbon film), particularly, depending upon whether the carbon film present on the applied side of the higher potential during the driving contains nitrogen.
Specifically, an electron-emitting device of the present invention is an electron-emitting device comprising first and second carbon films laid on a substrate, and first and second electrodes electrically connected to the respective carbon films, wherein a higher voltage is applied to the second electrode than to the first electrode and wherein the carbon film connected to the second electrode comprises nitrogen.
Another electron-emitting device of the present invention is an electron-emitting device comprising a carbon film and first and second electrodes electrically connected to two ends of the carbon film, wherein the carbon film comprises a gap located between the first and second electrodes and wherein a ratio of nitrogen atoms in the carbon film to carbon atoms in the carbon film is not less than 2/100 and not more than 15/100.
When the carbon-containing film (carbon film) comprises nitrogen, resulting physical properties are an increase of electron scattering coefficient and an increase of secondary emission coefficient of the carbon-containing film (carbon film). For this reason, the aforementioned electron emission efficiency can be increased when the carbon film connected to the electrode to which the higher voltage is applied during the driving (the carbon film where electrons are scattered) is made to contain nitrogen. Namely, with the electron-emitting device of the present invention, the device current If can be decreased, while the emission current Ie is increased.
However, the thermal stability and electric conductivity will be degraded with increase of the nitrogen content on the other hand.
For this reason, the electron-emitting device can be realized with high efficiency and excellent driving stability by controlling the ratio of nitrogen atoms to carbon atoms in the carbon-containing film (carbon film) (the number of nitrogen atoms/the number of carbon atoms) to not less than 2/100 and not more than 15/100.
Further, when the ratio of nitrogen atoms to carbon atoms in the carbon-containing film (carbon film) (the number of nitrogen atoms/the number of carbon atoms) is controlled to larger than 5/100 and not more than 15/100, the electron-emitting device can be realized with extremely high efficiency and excellent driving stability.
An electron source of the present invention is an electron source for emitting electrons according to an input signal, wherein a plurality of electron-emitting devices of the present invention described above are arrayed on a substrate; the electron source is arranged preferably in a configuration in which there are a plurality of rows of electron-emitting devices whose two terminals are connected to respective wires in each row and in which there is modulation means, or in a configuration in which a plurality of electron-emitting devices are connected in a matrix to a plurality of X-directional wires and Y-directional wires electrically insulated from each other.
The present invention also provides an image-forming apparatus comprising an electron source and an image-forming member and adapted to form an image according to an input signal, wherein the electron source is the electron source of the present invention described above.